Revert "Add "contains" method to Collection."

lib/compiler/implementation/lib/interceptors.dart

Index: lib/compiler/implementation/lib/interceptors.dart
diff --git a/lib/compiler/implementation/lib/interceptors.dart b/lib/compiler/implementation/lib/interceptors.dart
index 8aa6509f96bd68c22e525c77762359d8cec68f0e..680af43e4408e4c86110e683b17e77d774d02123 100644
--- a/lib/compiler/implementation/lib/interceptors.dart
+++ b/lib/compiler/implementation/lib/interceptors.dart
@@ -516,15 +516,10 @@ concat(receiver, other) {
 }
 
 contains$1(receiver, other) {
-  if (receiver is String) {
-    return contains$2(receiver, other, 0);
-  } else if (isJsArray(receiver)) {
-    for (int i = 0; i < receiver.length; i++) {
-      if (other == receiver[i]) return true;
-    }
-    return false;
+  if (receiver is !String) {
+    return UNINTERCEPTED(receiver.contains(other));
   }
-  return UNINTERCEPTED(receiver.contains(other));
+  return contains$2(receiver, other, 0);
 }
 
 contains$2(receiver, other, startIndex) {